LISBON (Reuters) - Portugal's main opposition party, the Social Democrats, reached an agreement late on Thursday with the right-wing CDS-PP for a pre-electoral alliance as they seek to bolster their chances of winning the March general election.
Portuguese Prime Minister Antonio Costa, from the Socialist Party (PS), resigned on Nov. 7 over an investigation into alleged illegalities in his government's handling of lithium, hydrogen and data centre deals.
President Marcelo Rebelo de Sousa called a snap election for March 10.
The Social Democrats (PSD), led by Luis Montenegro, said the pre-electoral agreement, to be signed on Sunday and known as the Democratic Alliance (AD), had "historical inspiration and symbolism".
Most opinion polls put the PS, now led by Pedro Nuno Santos, neck and neck with the PSD but a survey released on Jan. 1 showed the Socialists with 34.1% of the vote compared to the PSD's 24.8%. The new alliance should strengthen the Social Democrats' position.
A similar coalition in Portugal in 1979 won an outright parliamentary majority the following year.
The alliance would also guarantee the right-wing CDS-PP's return to parliament after it failed to elect any lawmakers in the last general election in 2022, its leader Nuno Melo said.
Political scientist Adelino Maltez said that even though the CDS-PP failed to secure seats in 2022 the party "was not dead", still had a level of public support and had a media presence: "That's what convinced Montenegro."
Many analysts fear a post-election stalemate given the rise of the populist, anti-establishment party Chega.
"A true renewal of the AD is impossible because the birth of Chega completely changed the political framework," said Maltez.
Established in 2019, the far-right Chega emerged as Portugal's third-largest parliamentary force, winning around 7% share of the vote in the 2022 election. Monday's Aximage poll showed support for Chega could now grow to 16.3%. PSD has ruled out making it an ally.
The PS has been in power since 2015 and Costa's first four-year mandate was won through a far-left alliance with the Left Bloc and Communists.
Nuno Santos successfully coordinated support for that alliance and has not ruled out a similar one this time. Left Bloc leader Mariana Mortagua has also signalled their willingness to negotiate an alliance.